CHAPTER TENTH. 

 EMBRYOLOGY. 



SECTION I. 



OF THE EGG. 



271. THE functions of vegetative life, of which we have 

 treated in the preceding chapters, namely, digestion, circu- 

 lation, respiration and secretion, have for their end the pre- 

 servation of the individual. We have now to treat of the 

 functions that serve for the perpetuation of the species, 

 namely those of reproduction (200). 



272. It is a law of nature that animals as well as plants 

 are preceded only by individuals of the same species ; and 

 vice versa, that none of them can produce a species differ- 

 ent from themselves. Reproduction in animals is almost 

 universally accomplished by the association of individuals of 

 two kinds, males and females, living commonly in pairs or 

 flocks, and each of them characterized by peculiarities of 

 structure and external appearance. 



273. As this distinction prevails throughout the animal 

 kingdom, it is always necessary for obtaining a correct and 

 complete idea of a species, to bear in mind the peculiarities 

 of both sexes. Every one is familiar with the differences 

 between the cock and the hen, the lion and the lioness. 



